Effect of annealing and atmosphere on the structure and optical properties of Mg_2TiO_4 thin films obtained by the radio frequency magnetron sputtering method

摘要

In this article, nanocrystalline Mg_2TiO_4 (MTO) thin films were deposited on quartz substrates with a thickness ranging from 200 to 300 nm at ambient temperature by the radio frequency magnetron sputtering method. These films were kept under O_2 standard cubic centimeters per minute (SCCM) and, post deposition, annealing in air at 500℃ for 1 h. The structure of the sintered target and films were analysed by X-ray diffraction (XRD). The XRD patterns indicated that these films are amorphous structurally, and annealing process induces the formation of crystalline phase. The microstructure and surface morphology of the MTO films were studied by field emission scanning electron microscopy and atomic force microscopy. The post-deposition annealing resulted in an amorphous-crystalline phase transition in the films, which is accompanied by an increase in the refractive index and decrease in the optical bandgap. The annealed films exhibit a refractive index of 1.98-2.03 (at 600 nm) with an optical bandgap values between 4.44 and 4.58 eV. The increase of refractive index for annealed films can be attributed to increase of crystalline nature and packing densities. The O_2 SCCM and annealing also greatly affected the photoluminescence spectra. In addition, the characteristic emission sharp peak and shoulder peaks at 357, 409 and 466 nm were detected.